1. Field of the Invention
The present invention relates to the field of paper manufacture and in particular to air-laid processes.
2. Description of the Prior Art
Traditionally, paper is manufactured by depositing fine fibers in a very dilute suspension in water on a fine mesh screen. The prime prerequisite is a large quantity of water in order to form the dilute suspension. Thereafter, the water is removed by varying types of drying processes all of which ultimately use large amounts of energy. In addition, present environmental considerations no longer allow the dumping of such removed water as waste, but require recirculation. The expended recirculated water must be treated and purified before reuse. This adds to the amount of energy normally required to produce the paper.
Paper formation is generally accomplished by bonding between tiny fibriles on the paper fibers. In the case of celluslosic fibers, paper strength is primarily provided through hydrogen bonding at the points of interfibrile contact. In the case of noncellulosic fibers, such as mineral, glass or plastic fibers, a resin is added to achieve the bonding at the interfibrile contact.
In order to overcome these shortcomings, the prior art has devised methods in which the fibers are dispersed in air and then deposited to form a paper web. However, since there is no or little hydration of cellulosic fibers which are thus air deposited, resultant air-laid mat exhibits very little strength since hydrogen bonding occurs, if at all, to a minimal extent. Therefore, most air-laid papers, even when composed of cellulosic fibers, require the addition of a resin binder to provide interfibrile bonding. One such prior art process is shown by Iannazzi, "PROCESS FOR DRY FORMING PAPER", U.S. Pat. No. 3,906,064, which shows air dispersed fibers introduced into a circulating loop. The fibers are circulated at a predetermined velocity and then withdrawn. Withdrawn fibers are then directed against a paper making wire screen upon which the paper web is formed.
In Mills, "PAPER MANUFACTURE", U.S. Pat. No. 2,810,940, a small amount of moisture is added to the fibers by opening a valve whereupon the fan draws air from over a water tank so that moisture laden air is mixed with the paper stock and the fibers take on the moisture. The air or water may be heated to enhance moisture absorbtion by the fibers. A suction device operates to assist intermingling of the fibers to remove moisture from the paper stock as it is air delivered to the belt. Paper making stock is continuously supplied from a supply vat by a continuously rotating screw onto an endless conveyor belt. A delivery nozzle extends from a housing and terminates in a wide delivery outlet. A Yankee dryer is adjacent to the delivery outlet and to the belt. In addition, pressure rollers are disposed on each side of the belt to press the fiber carried on the belt.
Although not a waterless process, the use of water vapor in a heated air dispersed cellulosic fibers are air-laid upon a mat forming belt and then later dried by suction, and pressing by conventional means. A similar water bearing air-laid process for making paper is discussed by Dunning et al, "APPARATUS FOR FORMING AIR LAID WEBS", U.S. Pat. No. 3,825,381, wherein a water spray is used to wet wood fiber which is air laid and then pressed to form a bonded web.
Thus, the prior art has utilized air-laid fibers in combination with various forms of water spray or moisture laden air in attempt to form the hydrogen bonds between the fibriles. However, the strength of the paper thus formed is still not acceptable for many applications and the amount of moisture which may be added, although less than traditional wet processes, is still great. If substantial hydrogen bonding is to be accomplished, large enough amounts of water are used so that the amount of energy then later required to dry the air-laid paper is still significant.
What is needed, then, is a methodology for the dry manufacture of paper in which a high degree of hydrogen bonding can be obtained in cellulosic fibers with a minimal amount of moisture used in a substantially dry air-laid paper manufacturing process.